The present invention relates to a camera video signal processing circuit for processing camera video signal in monitoring system and the like and displaying to a monitor or TV receiver and the like, and more particularly, to a still picture circuit in TV receiver in which, in case when video signal is not inputted from video camera, last picture is held whereby enabling to display as a still picture
FIG. 1 is a camera video signal processing circuit used in conventional monitoring systems and the like, as shown in FIG. 1, the circuit comprises:
luminance/color difference signal and synchronous signal separator 1 which receives video signals VI from a video camera whereby separating horizontal synchronous signal HS, vertical synchronous signal VS, luminance signal Y and color difference signals R-Y, B-Y;
analog switching means 2 for selecting said luminance signal Y and color difference signals R-Y, B-Y;
analog/digital converter 3 for converting output signal of said analog switching means 2 to digital signal;
encoder 6 for encoding the selection state of picture holding switch SWl and refresh switch SW2;
controller 4 which receives said horizontal and vertical synchronous signals HS, VS and output signal of encoder 6, and controlling the driving of said analog switching means 2 and said analog/digital converter 3, and receiving the output signal of said analog/digital converter 3 whereby storing to RAH 5 and outputting;
digital/analog converters 7-9 for converting the digital luminance signal Y and color difference signals R-Y, B-Y outputted from said controller 4 to analog signal;
synchronous signal generator 10 for generating horizontal synchronous signal HS, vertical synchronous signal VS, color burst signal CB and blanking signal BS; and
encoder 11 inputs output signal of said synchronous signal generator 10 and output signal of said digital/analog converters 7-9, the operating process of such a conventional circuit will be described in below.
When video signals VI are inputted from a video camera through coaxial cable, said video signals VI are separated into horizontal and vertical synchronous signals HS, VS, luminance signal Y and color difference signals R-Y, B-Y at the luminance/color difference and synchronous signal separator 1 whereby being outputted, and said horizontal and vertical synchronous signals HS, VS are applied to the controller 4, and thereby becoming to operate as control pulse in case of recording a picture data to the RAM 5 at said controller 4.
And, said luminance signal Y and color difference signals R-Y, B-Y are sequentially selected at the analog switching means 2 according to the selection control signals SL1, SL2 of controller 4 whereby being outputted, that is, the selection control signals SL1, SL2 are repeatedly outputted from the controller 4 in the sequence of "00".fwdarw."01".fwdarw."10".fwdarw. "11".fwdarw."00", accordingly said luminance signal Y and color difference signals R-Y, B-Y inputted to the input terminal a1-a4 of the analog switching means 2 are repeatedly selected in the sequence of Y.fwdarw.R.fwdarw.Y.fwdarw.Y.fwdarw.B.fwdarw.Y.fwdarw.Y to thereby be outputted, thus the signal outputted from the analog switching means 2 is converted to digital signal of M bits in synchronous with sampling signal CS of the controller 4 at the analog/digital converter 3 to thereby be applied to the controller 4. At this moment, the controller 4 outputs write control signal of high potential to its write terminal WR whereby making the RAM 5 to the write state, and designating the address of said RAM 5 through address bus AB, and becoming to record the digital signal inputted as above description through data bus DB, and outputting the read control signal to its read terminal from the controller 4 whereby the RAM 5 is made to the read state, and the address of said RAM 5 is designated and accordingly the digital signal recorded as above description to said address is read out to thereby be outputted.
Thus, the signals outputted from the controller 4, that is, the luminance signal Y and color difference signals R-Y, B-Y are converted to analog signal at the analog/digital converters 7, 8, 9 to thereby be applied to the encoder 11, and at this moment, horizontal and vertical synchronous signals HS, VS, color burst signals CB of 0.degree. and 90.degree., and blanking signal BS are generated at the synchronous signal generator 10 to thereby be applied to said encoder 11, and according to this, the output signals Y, R-Y, B-Y of the digital/analog converters 7, 8, 9 and the output signals HS, VS, CB, of the synchronous signal generator 10 are synthesized at the encoder 11 to thereby be made into synthetic video signal VO and thereafter being displayed on a monitor or a TV receiver.
On the other hand, when the picture holding switch SWl is short-circuited, said short-circuited state of the picture holding switch SWl is encoded at the encoder 6 to thereby be applied to the controller 4, and according to this, the controller 4 reads out only the digital signal finally recorded to the RAM 5 whereby it is outputted, and therefore the holding picture is displayed on the monitor or the TV receiver, and when the refresh switch SW2 is short-circuited, said short-circuited state of the refresh switch SW2 is encoded at the encoder 6 to thereby be applied to the controller 4, and according to this, the controller 4 is operated as above description and thereby the motion picture becomes displayed.
However, in such conventional apparatus, it is made into a still picture only in case when the picture holding switch is short-circuited, and accordingly, in case when video signal is not inputted due to the reason that coaxial cable of video camera is cut off and the like, there has been a problem that final picture can not be recognized.